Photovoltaic power generators having a power storage function are useful as an apparatus for bringing electric equipment into operation at places where commercial electric power is not distributed. An example of compact photovoltaic power generators having a power storage function is an apparatus supplying electric power to garden lights used in residential gardens where electrical wiring is not installed, that is, an apparatus storing electric power of solar cells during the daytime and discharging and supplying electric power to the lights during the night.
FIG. 3 is a diagram showing a configuration of a conventional interconnection system for a photovoltaic power generation system having a power storage function.
Referring to FIG. 3, this interconnection system includes a solar battery 101, a storage battery 102, an alternating current (AC) load 103, and a power converter 104. In operation of the interconnection, power converter 104 outputs current to a commercial power system of AC (Alternating Current) 200V in place of AC load 103.
In such an interconnection system for a photovoltaic power generation system having a power storage function, electric power from solar battery 101 can be stored in storage battery 102 via power converter 104 during the daytime, even when the commercial power system is failed. On the other hand, during the night, power is discharged from storage battery 102 through power converter 104 so that power is supplied to AC load 103 at home. Since AC load 103 generally operates at AC 100V, power converter 104 in this case converts DC (Direct Current) voltage from the storage battery and the solar battery into AC 100V for output.
Here, in recent years, electric equipment that consumes much power, such as air conditioners and electromagnetic cookers, are increasing as AC load 103 desired to operate at a time of power failures in ordinary households. Such electric equipment that consumes much power may require large power particularly when being started. In such a case, in order for AC load 103 to be started stably, it is necessary to instantaneously supply large starting power from power converter 104 to AC load 103.
As a conventional technique that solves the similar problem as above, Japanese Patent Laying-Open No. 2006-29142 (Patent Document 1) discloses a vehicle engine start control apparatus as follows. Specifically, an engine start control apparatus for a vehicle installed with an engine generating driving force of the vehicle and an engine starting apparatus receiving power supply to start the engine includes first and second power storage apparatuses capable of supplying the stored power to the engine starting apparatus and a starting current control unit provided between the first and second power storage apparatuses and the engine starting apparatus to supply operating current for the engine starting apparatus by means of at least one of the first and second starting current from the first and second power storage apparatuses, respectively. The starting current control unit controls the proportion of the first and second starting current of the operating current, depending on a state of the vehicle at a time of engine start. Because of such a configuration, in a vehicle in which operating current can be supplied to the engine starting apparatus by both the first power storage apparatus (secondary battery) and the second power storage apparatus (capacitor), a proper balance of current supply from them can be attained depending on a vehicle state. Therefore, at a time of supplying operating current to the engine starting apparatus that consumes much power, an output voltage drop caused by excessive output current can be prevented in either power storage apparatus, thereby achieving smooth and stable vehicle operations.
Furthermore, Japanese Patent Laying-Open No. 2005-199739 (Patent Document 2) discloses voltage-dependent vehicle-mounted equipment as follows. Specifically, the voltage-dependent vehicle-mounted equipment is connected to an ACC (accessory) power supply of a vehicle and/or a battery, and a capacitor bank is connected to and charged by the ACC power supply and/or the battery to supply electric power to the voltage-dependent vehicle-mounted equipment when the electric power supplied to the voltage-dependent vehicle-mounted equipment becomes a prescribed value or lower. Because of such a configuration, it becomes possible to instantaneously supply electric power from the capacitor bank to the voltage-dependent vehicle-mounted equipment in response to a momentary power drop due to restarting of the engine of an idling stop vehicle. Therefore, it is possible to provide a voltage-dependent vehicle-mounted equipment immune to a momentary power drop and an environmentally-friendly automobile of good performance.    Patent Document 1: Japanese Patent Laying-Open No. 2006-29142    Patent Document 2: Japanese Patent Laying-Open No. 2005-199739